This bike, a 1975 R75/6, is the first BMW I bought and now has almost 106,000 miles on it. It is the first bike I rode more than 1,000 miles in one day back in 1976 and is the first build project I completed in 2010 and documented here:

I decided to do a “refresh” primarily because the paint work I did (my first time painting) failed due to my ignorance about the importance of using primer and paint from the same manufacturer. Also, I only did spot touch up painting on the frame so it’s time to strip the bike down to the frame for new powder coating.

I have several projects that I didn’t get to during the build. One of these is replacing the timing chain which I document here. My bike has the duplex, dual row chain, while starting in the 1979 model year, the timing chain is a single row chain with a hydraulic chain tensioner. This procedure should help you replace a /5, /6 or /7 series timing chain, but some of the parts will be different as I note later.

Since I stripped the bike I have the engine out of the frame, but most people will do this work with the engine in the frame. Although it is an option to remove the front wheel and forks to have clear access to the front of the engine, I think the work can be done without removing them.

Resources

Before starting this project, I reviewed material available on the Airheads Beemer Club site, www.airheads.org: I believe you can access the links below even if you are not a member, but consider joining this group if you want to contribute to the Airhead culture. I read material on Bob Fleischer’s web site, and I posted a number of questions to the Micapeak Airheads forum whose members are legend for providing thoughtful advice and encouragement. You should add these resources to your toolkit as they are authoritative with valuable information.

In particular, I want to acknowledge Ron Cichowski, Tom Cutter, Bob Fleischer, Doran Shields, Marten Walkker and Eric Zwicky on the Micapeak Airheads forum for answering my questions. Also, a local Colorado Airhead, Don Wreyford, came by to kibitz and help with the disassembly process. Don has always been generous with his time and knowledge. And, my youngest son, Branden, shown in many of the photos with the electric yellow shirt, helped me on the entire project with wrenching, picture taking, and good ideas and advice when we needed to stop and reconsider what we should do next. He is turning into an accomplished Airhead wrench and lover of Bavarian iron.

Parts and Tools

My bike was manufactured in May 1975 so it has the continuous loop, duplex, or double row, chain. I purchased a new timing chain with a master link made by Iwis that is a popular upgrade. If I replaced it with the original continuous loop chain, I have to remove the cam shaft which is much more effort.

MAX BMW provides the Iwis chain, but the master link included uses two very small C-clips on the ends of the pins instead of a single fish plate that is commonly found on motorcycle chains. MAX supplies a master link with a fish clip which I purchased. Faced with the choice of installing the two small C-clips or a single larger fish clip on the backside of the chain where there is very limited visibility and clearance to work, I voted for the single fish clip. I figured trying to install a bigger part once would be easier then two small parts, and the number of parts–and potential for the master link to come loose over time–is reduced.

The crankshaft sprocket (11 21 1 250 198) is one-half the size of the camshaft sprocket and that means it wears more rapidly and should be replaced when replacing the timing chain. There is a bearing on the end of the crankshaft that I call the crankshaft nose bearing (07 11 9 981 722) and it too should be replaced when replacing the crankshaft sprocket. I did not order a camshaft sprocket based on comments I read that it does not wear as fast as the crankshaft sprocket. I found it in very good condition when I inspected it.

One other detail is the year of my bike and the size of the camshaft seal. Up to 09-1975, a small camshaft seal (11 14 1 261 193) is used and after that date (essentially the 1976 model year) a larger camshaft seal is used. Be sure to confirm the year of manufacture of your bike so you order the proper size camshaft seal.

There is a gasket (11 14 1 338 428) that seals the oil inside the inner timing cover and also two small gasket “donuts” (11 14 1 338 429) that mount on the top two bolts holding the inner timing cover to the engine. The donuts don’t seal oil, but do ensure the inner timing cover remains square to the engine case when the bolts are tightened. If you don’t install these two donut gaskets, the inner timing cover will leak oil.

I replaced the rubber grommets that go around the engine wiring harness exiting the timing chest and the one on the top engine cavity where the (+) battery terminal exits from the top of the engine. These are rubber and last only so long.

Below is my parts list for this project.

Parts List

Part No.

Description

Qty

11 31 1 250 258B

MASTERLINK CHAIN 1970-78
[MAX Part No]

1

11 31 1 250 2587

MASTERLINK FOR DUPLEX CHAIN W/ FISH PLATE
[MAX Part No]

1

11 14 1 337 654

CRANKSHAFT SEAL – 28X47X7

1

11 31 1 265 455

CHAIN TENSIONER ARM

1

11 31 1 253 188

CHAIN TENSIONER SPRING

1

07 11 9 981 722

GROOVED BALL BEARING – 160 07

1

11 21 1 250 198

CRANKSHAFT SPROCKET

1

11 14 1 338 428

INNER TIMING COVER GASKET

1

11 14 1 338 429

WASHER-GASKET

2

61 13 1 352 095

RUBBER GROMMET

2

11 14 1 261 193

CAMSHAFT SEAL – 12X25X8 (to 09/75)

1

Optional Parts

I decided to replace a number of engine electrical components. I found a kit at Euro Motoelectrics that includes a new alternator rotor, alternator brushes, diode board, crankshaft seal and electronic voltage regulator at a very reasonable price. They also have a kit with new wires for the three alternator phase wires that go to the diode board, the “red” wire from the right side of the diode board to the starter solenoid and the black “Y” wire from the left side of the alternator to the left side of the diode board, and a ground wire for diode boards that have the rubber grommets which the R75/6 doesn’t have.

Part No.

Description

Qnty

BOALT-BMWPLUS

Bosch Alternator Kit / EnDuraLast

1

BOALT-HAR063

Wiring Harness, Diode Board

1

Tools

In my opinion, this work requires special tools to remove the crankshaft sprocket and crankshaft nose bearing, installing the crankshaft nose bearing, and potentially the inner timing cover.

I purchased specialized airhead tools from Cycle Works in the past and have been very pleased with the quality, ingenuity and ease of use. I opted to purchase the complete duplex chain engine tool set, Airhead Engine Mulit-Tool – Duplex Chains. But, for this project, you only need the Airhead Engine Front End Tool kit. These tools from Dan Neiner at Cycle Works were once again perfect for this project.

I use the Cycle Works alternator rotor extractor bolt which is a special hardened bolt to remove the alternator rotor. An ordinary bolt or mild steel rod will mushroom inside the threaded crankshaft nose, and then you have a very expensive project on your hands.

Cycle Works BMW Stock Alternator Rotor Removal Bolt (Hardened)

I used seal pullers to remove the front crankshaft seal and the camshaft seal, and an alternator rotor hardened extractor bolt. I also needed a 260 watt soldering iron to replace the alternator brushes, but you only need one if you wish to replace the brushes when you reinstall the alternator.

Overview of Procedure

The project requires disassembly as follows:

Remove Battery Ground and Engine Covers

Remove Engine Electrical Components

Remove Inner Timing Cover

Position Engine at TDC and Add Alignment Mark

Remove Camchain Tensioner Arm and Spring

Remove Timing Chain

Remove Crankshaft Nose Bearing and Sprocket

Remove Inner Timing Cover Gasket and Clean Surfaces

Remove Front Crankshaft and Camshaft Seals

Assembly requires the following:

Install New Crankshaft Sprocket

Install New Crankshaft Nose Bearing

Install New Timing Chain With Master Link

Install New Timing Chain Tensioner Arm and Spring

Install New Inner Timing Cover Gasket and Two “Donut” Gaskets

Install Crankshaft Front Seal and Camshaft Seal

Install Inner Timing Cover

Install Engine Electrical Components

Disassembly Procedure

Remove Battery Ground and Engine Covers

Since I already stripped the bike to the frame, the engine is out and I put it on my workbench.

Ready To Start – Front and Top Covers Removed

If you are working with the engine in the frame, disconnect the battery ground wire from the engine block. Then remove the three Allen bolts that hold the front engine cover on. Remove the top engine cover that has the rubber air intake from the engine. There are two Allen bolts holding it on and it can be rolled to the right side and slipped off the engine block without bumping against the frame top member.

Remove Engine Electrical Components

I start at the bottom where the points are and work to the top ending with the diode board. I installed a Dyna III electronic ignition but it uses the original timing advance unit and has a points plate that mounts like the original points plate.

Remove Timing Advance and Points Plate

Remove the 10 mm nut holding the points advance unit onto the camshaft and pull the advance unit off the camshaft.

Removing Nut Securing Timing Advance Unit

Removing Timing Advance Unit From Cam Shaft

Dyna III Magnet Mounted on Stock Timing Advance Cam

Before removing the points plate, I scribe a mark on the edge of the engine case and the points plate so when I replace the points plate, the engine timing should be close enough to start the engine without having to statically time it. To remove the plate, remove the two screws at the top and bottom of the plate. Note, I replaced the screws with Allen head bolts which make it easier to adjust the points plate while the engine is running.

Dyna III Points Plate Secured by Allen Bolts at 12:00 and 6:00

Dyna III Points Plate Removed

Last, I remove the condenser and the strap that holds it on the inner timing cover. The Dyna III electronic ignition does not use the condenser, but I keep it installed so I can easily install the old points should the Dyna III fail.

Condenser and Mounting Strap Removed

As I remove parts, I place them in plastic zip-lock bags and label them. This makes it much easier to find the parts during reassembly and prevents small washers and nuts from getting lost. I also clean up fasteners and parts before I put everything back together. No need to let grit, dirt and schmutz sully your fine workmanship 😉

Storing Parts in Labeled Sandwich Bags

Removing Alternator

I label all the wires as I remove them so it will be easy to attach them when I reinstall the electrical components.

Removing (3) Allen Bolts from Alternator Housing: 2:00, 7:00, 11:00

After I remove all the wires from the alternator terminals, I remove the three Allen bolts that secure the outer cover. The cover fits into a raised boss. I use a large screw driver placing the blade ONLY on the edge of the alternator cover being careful not to hit any of the wires and with the shaft against the outer edge of the inner timing cover gently leverage it out of the boss. There are three bosses around the circumference of the cover, so I move around to each of them to evenly lever the alternator cover out.

Carefully Leveraging Alternator Housing Off Bosses (Don’t Nick Wires)

Move Around the Alternator Housing To Loosen Uniformly

The cover is connected to the stator wire bundle underneath so be careful to remove both of them as a unit to avoid putting strain on the stator wires that connect to the cover.

Alternator Stator and Housing Removed as A Unit

There are various models of the alternator for airheads, and each has different sized stator and rotor parts.

Original Bosch Alternator

When the stator and alternator housing are removed, the alternator rotor is exposed. It mounts on a tapered nose on the end of the crankshaft. The copper bands on the front are the slip rings that send the power to voltage regulator and the battery for charging.

Since the rotor is subject to rotating forces and heat, it can fail in time. Mine has been in place for 106,000 miles and 40 years, so I am replacing it.

I remove the Allen bolt in the center of the rotor. As I can’t put the bike in gear to prevent the crankshaft from rotating, I use a small impact driver to get the bolt loose. Note there are two sets of threads the bolt has to pass through; the threads in the crankshaft nose and the threads in the rotor. As the bolt threads completely come out of the crankshaft nose the bolt will briefly move toward you and then engage with the threads in the rotor.

Alternator Allen Bolt Screws Into Crankshaft Nose

Small Electric Impact Driver

Alternator Bolt Removed

A special hardened bolt is used to press the rotor off the tapered nose of the crankshaft. I got this one from Cycle Works.

Cycle Works Hardened Bolt for Stock BMW Alternator Rotor Removal

Note that the threads have been removed from the beginning of the bolt so it will pass by the threads in the crankshaft nose. The threads of the bolt engage with the threads in the rotor and the end of the bolt presses on the inside of the crankshaft nose forcing the rotor off the crankshaft. For this reason, it is VERY IMPORTANT that a hardened bolt be used to press the alternator rotor off the crankshaft. A standard bolt, or a soft steel rod can mushroom inside the crankshaft nose. If that happens, you now have a very expensive project on your hands.

Since I can’t put the bike in gear to prevent the crankshaft from turning, I use an oil filter wrench on the outside of the rotor to keep if from spinning as I remove the rotor with the hardened bolt. It is a good idea to put a dab of anti-seize or grease on the threads and nose of the rotor puller bolt to lubricate them.

Oil Filter Wrench

Cycle Works Hardened Bolt Threaded Into Alternator Rotor Threads

Oil Filter Wrench Securing Rotor While Tightening Rotor Removal Bolt

The rotor can pop off with some force so be ready to catch it and prevent it from falling on the floor.

Alternator Rotor Fits on Tapered Crankshaft Nose

Original Alternator Rotor

Remove Diode Board

The diode board has wire connections on the left and right sides and on the back of the board. The black wire on the left side goes to the “Y” terminal on the alternator cover. I remove it as I am replacing it with a new one. The diode board is secured with four Allen bolts.

Remove (4) Allen Bolts Securing Diode Board

Here are the wires on the back. In the center are three wires that connect to three terminals on the lower right side of the alternator cover at the 5:00 position and I am replacing them. The center wire has two blue leads. I label these wires and then remove them from the diode board terminals.

Connections on Back of Diode Board

There are two wires on the right side of the diode board. The inner one has red insulation and has a smaller spade while the outer wire is black and has a larger spade. Note the red wire boot has gotten hot enough to melt. I am replacing it.

(2) Wires on Right Side of Diode Board (Note Melted Insulation)

Melted Boot of Red Wire on Right Side of Diode Board

Note the numerous labels on the wires I removed from the engine electrical components. You would be amazed how much detail you can forget after a day particularly when you are a “grey beard” like me ;-).

Engine Electrics Harness with Labels

I remove the three wires that go to the starter solenoid found under the top engine cover. The red wire from the smaller spade on the right side of the diode board has a ring terminal and mounts on the large solenoid terminal with the large diameter black battery (+) cable.

Red Wire From Diode Board Goes to Starter Solenoid Screw Terminal

The black wire comes off a spade terminal on the starter solenoid.

Black Wire with Spade Connector on Starter Solenoid

I remove the engine electrical wiring harness.

Engine Electrics Harness Removed With Labels

I am now ready to remove the inner timing cover.

Remove Inner Timing Cover

When I’m not sure what to expect with bunch of fasteners, I take a piece of cardboard and draw an outline of the part and then insert the fasteners in order. It turns out the (9) Allen bolts are the same length as are the (3) Allen nuts.

Cardboard for Storing Bolts in Correct Locatio

Bolts and Nuts in Bolt Location Card

With all the fasteners removed, I setup the Cycle Works tools to pull the inner timing cover.

Inner Timing Cover Fasteners Removed

The tools consists of various parts that are used for multiple operations. The instructions show how they go together and provide brief guidance on how to remove / install the parts.

From left to right is the Aluminum plate, inside it a hardened bolt, the steel puller body and the puller bolt. An important part is a hardened bolt that threads into the nose of the crankshaft. It prevents the puller from damaging the crankshaft.

Hardened Bolt to Protect Crank Nose

The hardened bolt threads into the crankshaft, but only a couple threads engage. I put some masking tape on the taper of the crankshaft nose to protect it from scratches while I work.

Protecting Crank Nose and Crankshaft Taper

The three alternator cover bolts are used to secure the aluminum plate to the inner timing cover.

Puller Plate with Alternator Bolts

The puller body has a groove cut on one side and the aluminum plate has a raised boss that fits inside the groove.

Puller Body and Puller Plate (Back Side)

Orientation of Puller Body in Puller Plate

As shown here, the large bolt with the round bearing on the end threads into the center of the puller body and presses on the hardened bolt in the crankshaft pulling the inner timing cover off the outer race of the crankshaft nose bearing.

Orientation of Puller Body on Crank Nose

Before I insert the large bolt into the puller body, I put some anti-seize on the inside threads to lubricate the large puller bolt and prevent galling and thread damage.

Anti-Seize on Puller Body Threads, I Got Carried Away, Just a Little Is All You Need

Here is the inner timing cover puller assembled and ready to go.

Cycle Works Inner Timing Cover Removal Tool

Cycle Works Inner Timing Cover Removal Tool

Cycle Works Inner Timing Cover Removal Tool

Before I use it, I put a dab of anti-seize on the exposed thread of the large puller bolt for good measure.

Anti-Seize on Puller Bolt Threads

I plan to use two crescent wrenches to pull the cover, but as my son finger tightened the larger center bolt, the cover moved off the crankshaft nose bearing. This happens sometimes.

Finger Tight and The Inner Timing Cover Came Loose

Timing Cover Sliding off Crankshaft Nose Bearing and Camshaft

As the cover comes free, the gasket is exposed and there is a small amount of oil in the bottom of the cover so have a rag handy to catch the oil.

Still in the cover are the front crankshaft seal and underneath it the smaller camshaft seal. I remove those later.

Old Front Crankshaft Seal

Here’s what is inside the inner timing cover, the object of our disassembly, the timing chain, tensioner arm and spring, and just under the horizontal cylinder which is the oil pressure relief valve, the crankshaft nose bearing and behind it the crankshaft sprocket. Note the masking tape on the crankshaft taper. I added that to protect it from getting scratched while working inside the inner timing cover.

What’s Under the Inner Timing Cover

Add Timing Marks to Crankshaft and Camshaft Sprockets

Before I go any farther, I mark visible the timing marks on the crankshaft and camshaft sprockets. I had put the engine at Top Dead Center (TDC) which is the “OT” mark on the flywheel before wiring up the pistons to protect the engine case from nicks. But, when doing this with the engine in the frame, just put the engine is 2nd or 3rd, rotate the rear wheel until “OT” shows next to the mark in the engine case.

NOTE:The cam shaft rotates 1/2 turn for each revolution of the crankshaft. Consequently, you may not be see the scribe mark on the tooth of the camshaft sprocket as that tooth can be at the 6:00 position instead of the 12:00 position. If so, rotate the engine one more revolution and the camshaft sprocket scribe mark should be visible. If you can’t find a scribe mark on the camshaft sprocket, then mark it as I did with white paint or white-out so you can be sure to preserve the crank and cam alignment correct. If you are off a tooth, it will impact setting the ignition timing.

Top Dead Center (OT) Set

I’m not sure if I see a faint scribe mark on the camshaft sprocket, so I paint a mark on it and as insurance, I add a couple of punch marks as well. It’s possible the scribe mark oon the camshaft sprocket is at the 6:00 position, and since I wired up my connecting rods, I don’t want to rotate the engine to see if that’s the case. As I am replacing the crankshaft sprocket, there is no need to mark it.

Paint Mark on Cam Sprocket 12:00 Position

Adding Pin Prick Marks to Cam Sprocket at 12:00 Position

Remove Timing Chain Tensioner Arm and Spring

Close Up of Timing Chain Tensioner Arm and Spring

The timing chain tensioner arm is held on the pivot shaft with a C-clip.

C-Clip on Chain Tensioner Arm Post

It’s a good idea to cover the openings in the engine casting behind the crankshaft and camshaft sprockets so the C-clip doesn’t pop off and go inside the engine. I used masking tape but it was hard to install and remove. In the future I would cut a piece of paper long enough to cover the openings so the ends extend to the edge of the engine case and tape the ends down.

I use a magnet near the C-clip to catch the C-clip if it pops off the pivot pin. Once the clip is removed, the tensioner arm slides off the pivot pin.

Removing C-Clip on Tensioner Arm Post

Removing Chain Tensioner Arm From Pivot Post

One of the four nuts that secures the front crankshaft bearing holder, at the bottom right, holds the tensioner spring. I remove it and the washer underneath along with the spring.

One Nut Holds Tensioner Spring

Chain Tensioner Spring, Washer and Nut

Remove Timing Chain

Be sure all the openings into the engine are covered or stuffed with rags. I use a Dremel tool with cutoff wheel to grind the pins off a link and to cut through the plate between the pins. So there will be a lot of swarf and debris and I don’t want it to get inside the engine.

Ready to Cut Off Old Continuous Timing Chain

I decided to choose a link that was on the crankshaft sprocket so if the cutoff wheel nicked a sprocket tooth it wouldn’t matter since I am replacing the sprocket. It is a tight fit for the cutoff wheel, so I placed it behind the chain link before turning it on so I wouldn’t nick the engine case.

Removing Link in Cam Chain with Dremel Cut Off Wheel

My son ran the Dremel and after a sufficient amount of sparks, we figured he had cut off the pins on the link.

Grinding Pins Of Link in Timing Chain

That said, we couldn’t get the link off, so he cut the front plate in half.

Cutting Front Plate of Link in Timing Chain

Then with a screw driver blade and a hammer he knocked on the back plate to drive the pins loose.

Driving Pins To the Back To Free Front Row

Now I rotated the engine enough so the cut link was off the sprocket. I used pliers to pull the chain ends off the pins by twisting the chain while pushing the pins to the back. This freed the front row of links and then I could pull the back row off the pins.

Chain Separated

Original Continuous Timing Chain Removed

There was a lot of shavings and debris so I used a magnet to collect as much as I could before removing the rags and coverings.

Metal Schwarf and Debris

Using Magnet To Clean Up Steel Shavings

The teeth of the crankshaft sprocket show wear but haven’t been worn to a knife edge yet.

Crankshaft Sprocket Teeth Are Worn Toward Top of Teeth

The camshaft sprocket teeth show no visible sign of wear.

Camshaft Sprocket Teeth

Camshaft Sprocket Teeth

Camshaft Sprocket Teeth

Remove Crankshaft Nose Bearing and Sprocket

At this point, the sprockets and the crankshaft nose bearing are exposed.

Timing Chain Removed Exposing Sprockets and Crankshaft Nose Bearing

Here are the parts of the Cycle Works tool used to remove the crankshaft sprocket and nose bearing.

At the top is a large diameter steel sleeve. Beneath it are two aluminum clam shells that fit inside the steel sleeve. At the bottom is the steel puller body with the large extraction bolt inserted.

One of the aluminum clam shells is inserted so the lip goes behind the back row of the crankshaft sprocket teeth. The puller body fits inside and in front of the nose bearing.

Positioning One Aluminum Clam Shell On Sprocket and Around Puller Body

Visually ensure that the clam shell edge is behind the back row of crankshaft sprocket teeth.

Verifying Aluminum Clam Shell Edge is Behind Rear Sprock

Insert the other clam shell half and hold them together.

Positioning Aluminum Clam Shells Around Puller Body

Now, slide the large steel sleeve over the two aluminum clam shells to hold them together.

Cycle Works Tool Installed

Visually inspect the back of the large steel sleeve. There is a recess on the front crankshaft bearing carrier and the sleeve should fit snuggly inside it.

Verify Large Steel Sleeve Is Positioned Correctly

I put a little anti-seize on the larger puller bolt threads near the the steel puller body and then used two crescent wrenches to pull the sprocket and nose bearing off the crankshaft. I did use any head since the crankshaft, sprocket and bearing are steel so they will expand at the same rate.

Using Crescent Wrenches to Remove Crankshaft Sprocket and Nose Bearing

It takes a number of turns to pull the sprocket and nose bearing off the crankshaft. I pushed the large metal sleeve back all the way and put a sharpie pen mark on an aluminum clam shell at the outside edge of the sleeve. That way I can verify the aluminum clam shells along with the sprocket and bearing are moving.

Removing Crankshaft Sprocket and Nose Bearing

When the bearing and sprocket are removed, they stay inside the clam shells, so remove the large steel sleeve and the clam shells to free them. Note the sprocket orientation. The long sleeve goes next to the engine block and the shorter next to the nose bearing.

Crankshaft Nose Bearing and Sprocket in Cycle Works Removal Tool

You can see some of the wear on the teeth of the crankshaft sprocket as a discoloration at the top of the teeth.

Old Crankshaft Sprocket Teeth Have Wear at Top of Teeth (Discoloration)

Here is a comparison of the new crankshaft sprocket (Left) and the original one (Right). You can see the amount the sprocket teeth are worn as a flat spot can be seen at the top of the teeth.

New (Left) Sprocket Wear on Teeth of Crank Shaft Sprocket (Right)

New (Left) Sprocket Wear on Teeth of Crank Shaft Sprocket (Right)

Here are the markings on the crankshaft nose bearing.

Crankshaft Nose Bearing Markings

Crankshaft Nose Bearing Markings

Crankshaft Nose Bearing Markings

Remove Inner Timing Cover Gasket And Clean

It is important that the mating surfaces of the timing cover and engine case are completely free of any gasket material. I use a sharp blade at a shallow angle to separate pieces of the gasket from the timing cover and the engine case.

CAUTIONYou don’t want to nick the sealing surface while removing the gasket or you will get oil leaks. The inner timing cover and engine case are aluminum which is soft. Go slow and consider using some of the gasket removers to soften it. Heat can also help soften the gasket material when it is stubbornly stuck to the metal.

Removing Old Gasket On Inner Timing Cover

I cleaned both sides of the inner timing cover and polished the edges so the case will look new when I install it.

It is important to clean the mating surfaces where the gasket goes on the engine block and the inner timing cover until they are shiny. I use acetone and steel wool to remove all traces of the gasket adhesive so the surface shines. Since the steel wool will shed small steel fibers, keep the holes in the engine cases sealed while doing this. Then I use compressed air to blow out any remaining bits from the engine case and timing cover.

Inner Timing Cover Mating Surface Clean and Shiny

Engine Mating Surface Needs A Bit More Work

Remove Front Crankshaft and Camshaft Seals

The seals will be replaced so I remove them from the inner timing cover with seal pullers.

Removing Crankshaft Seal

Removing Old Camshaft Seal

Assembly Procedure

Install New Crankshaft Sprocket

There is a Woodruff key that secures the crankshaft sprocket on the shaft. I inspect it for any nicks or damage and the make sure it is even in it’s slot.

Aligning Woodruff Key in Crankshaft

The new crankshaft sprocket has a timing mark on one tooth. But it will be hidden when the new nose bearing is installed, so I put some white paint along that tooth so I can see later. I suggest you extend the paint mark to the inside of that tooth so you don’t have to crane your neck to see it, DAMHIK 🙂 Note that the slot in the sprocket is at 9:00 when the tooth with the timing mark is at 6:00.

New Sprocket with Timing Orientation Mark at 6:00

The groove in the sprocket for the key will some small burrs on the edge from the machining. I use a small file and carefully clean up the end of the slot that is closest to the engine block, or on the end opposite the timing mark.

Edge of Keyway May Have a Small Burr Left From Machining

Removing Keyway Burr So It Will Easily Slide Past Woodruff Key

The crankshaft is discolored. I clean it up with some metal polish so it shine.

The Cycle Works tool includes parts to install the crankshaft sprocket.

At the top left is the puller body, underneath the small steel sleeve, in the middle are two washers and a needle bearing the goes in between them and on the right the pusher bolt with nut. I’ve read that if the sprocket is heated hot enough, it will slide onto the crankshaft without problems, but as insurance, I assemble the installation tool.

This shows how the two washers and needle bearing go together. The needle bearing allows rotation of the washers as the pusher bolt is tightened.

The small steel sleeve is machined differently on each end; one end has a recess cut into it and the other does not.

The face of the puller body has a raised ridge. The ridge fits inside the end of the small steel sleeve with the recess.

The pusher bolt has a small threaded end that threads into the crankshaft nose.

Here is the tool assembled for use. The small steel cylinder pushes on the face of the crankshaft sprocket and the pusher bolt is threaded into the crankshaft nose. The large nut is turned to push the sprocket onto the crankshaft and it presses on the washer-needle bearing sandwich which spins with the nut.

I heat the sprocket in the oven set to 325 F.

Heating Crankshaft Sprocket in the Oven-Top Side Goes Against Engine Block

While it heats, I put a small bit of lard on the crankshaft to lubricate it and help the sprocket slide on.

Kitchen Lard to Lubricate Sprocket and Nose Bearing Installation-Way More Than I Need

Light Lard Coating on Crankshaft

When my infrared thermometer shows the sprocket is hot enough, I pick it up with my welding gloves and quickly take it into the shop.

322 Deg Crankshaft Sprocket

I align the keyway with the woodruff key at and press it on as far as it goes. It slides right on with no trouble. I keep pressing firmly on the crankshaft until it cools; it takes about 30 seconds to cool to room temperature as the crankshaft is cold.

Crankshaft Sprocket Aligned on Woodruff Key

Quickly Pushing Crankshaft Sprocket On Crankshaft

Pushing Crankshaft Sprocket In Until Cool

Crankshaft Sprocket Cools in About 30 Seconds

I did not need the Cycle Works tool as this sprocket slide on very easily.

Install New Crankshaft Nose Bearing

I read that this bearing can also be slide on if heated. I was not able to get it to slide on. I tried heating it in the oven to 275 F but it cooled too quickly as I carried it out to the shop. I heated it in a pan with motor oil to 275 F in the oven (it starts to smoke so it’s stinky) to keep it hot while I carried it into the shop, but it still wouldn’t push on the crankshaft.

Heated Bearing Cools Too Quickly So I Can’t Slide It On 🙁

Pan With Oil and Nose Bearing For Heating

Hot Heated Nose Bearing and I Can’t Slide It On 🙁

So I use the Cycle Works Tool to install the nose bearing. The only change from the configuration for pushing on the sprocket is to reverse the small steel sleeve so the end with the recess goes against the inner bearing race. I don’t want to push on the outer race as it will damage the bearing cage. The inner race slides along the crankshaft so all the force used presses on it and not the bearing cage.

Installing Cycle Works Tool on Crankshaft Nose

I used some more lard on the exposed part of the crankshaft, centered the bearing on the shaft and then attached the Cycle Works tool to the crankshaft nose using the pusher bolt. Using two crescent wrenches, the bearing slide on the crankshaft until it was up against the sprocket.

Pushing Nose Bearing On With Cycle Works Tool

Pushing Nose Bearing On With Cycle Works Tool

I checked the face of the inner race to be sure it was flush with the end of the crankshaft to be sure both the sprocket and bearing are on all the way.

Crankshaft Nose Bearing and Sprocket Installed

Nose Bearing Installed Flush With End of Crankshaft

Install New Timing Chain With Master Link

At this point, getting the crankshaft and camshaft timing marks aligned is very important. I ensure the engine is set to TDC with the “OT” mark on the flywheel visible in the timing hole.

Set Engine to TDC “OT” Mark

I align the crankshaft sprocket timing mark at 6:00 and the camshaft sprocket timing mark at 12:00. The tooth on the crankshaft sprocket should point to the valley in the camshaft sprocket or inside the “V” paint mark I made.

Crankshaft Sprocket and Camshaft Sprocket Timing Marks Aligned at TDC

Since the crankshaft sprocket timing mark is hard to see with the nose bearing installed, I made another mark on the crankshaft nose so I can quickly verify the alignment when I install the timing chain. You can see the three marks inside the red ellipse in the picture below. The mark on the cam nose looks a bit out of alignment with the camshaft sprocket mark, but it’s due to being not exactly square with the engine when I took the picture.

Added Mark on Crankshaft Nose (Inside Red Ellipse)

The Iwis chain has a master link, but it uses two small C-clips on each pin. Since these are installed on the back side of the chain where I can’t see what I’m doing, I purchased a separate master link that uses a fish clip.

New Iwis Cam Chain with C-clips for Master Link Pins

Optional Master Link Kit with Fish Clip

Since this is a double row chain, there are two plates, one black and one bronze colored. These are different thickness with the thicker black one going in the middle and the thiner bronze one going on the back with the fish clip.

Master Link Middle Plate (Black) and Back Plate (Bronze)

Thickness of Master Link Middle Plate (Black)

Thickness of Master Link Back Plate (Bronze)

CAUTION Before you install the master link, make sure all the engine openings are covered. The master link plates and fish clip can and will fail or fly off and you don’t want them to fall inside the engine.

It is helpful if you can get comfortable when installing the timing chain. I sat on my stool at the workbench so I was relaxed. If you are doing the work with engine in the frame, if you have a lift, raise it to a comfortable level and get a stool of the proper height to be comfortable. If you don’t have a lift, then get some pillows to sit on the floor in a comfortable position. Having relaxed muscles and comfortable position will make this part of the work go quicker.

I install the chain with the location for the master link on the camshaft sprocket.

Using Sprocket Teeth to Hold Cam Chain In Place

There is no room to install the master link with the pins facing you. So I install it with the pins facing toward the engine block.

Starting Master Link From Front Side

I use a magnet to hold the black center plate so I can insert it and hold it in place while I push the master link through it.

Using Magnet to Hold Center Plate

Magnet Orients and Positions Center Plate

Master Link Installed Through Center Plate (Black)

I use the magnet to position the bronze plate on the back of the chain. This magnetizes the plate and it will stick to the master link pins and the engine block making it easy to align it with the master link pins.

Bronze Back Plate Orientation Before Pressing On Pins

I use two screw drivers, one below the plate to keep if from falling and the other behind the plate to push it on the pins. With one screw driver, I press against the plate to secure it on the pins.

Installing Bronze Color Back Plate With Screw Driver Blade

The fish clip goes on the chain so the open end, or tail, points in the opposite direction to the chain movement. The crankshaft rotates clockwise as you face the front of the engine. I am installing the fish clip on the right side of the chain, so chain motion is downward. That means the fish tail points upward.

I put some wheel bearing grease on the fish clip to help stick it to the master link while I position it with needle nose pliers and a screw driver. I use two screw drivers to position it on the bronze plate so the open end of the fish clip points up.

Wheel Bearing Grease on Fish Clip So It’s Sticky

Positioning Fish Clip On Back Plate and Master Link Pins

Positioning Fish Clip With Two Screw Drivers

This takes several tries. The idea is to position the fish clip with the lower pin inside the wide part of the clip and the tail just below the groove in the upper pin. One time the fish clip falls behind the camshaft sprocket. I couldn’t get the head of the magnet behind the sprocket. So I use a screwdriver with the magnet attached to magnetize it so I can go fishing for the fish clip. I hooked it 🙂

CAUTION:There are holes behind the camshaft sprocket that go inside the engine. That’s why blocking the holes off before installing the chain is very important.

How To Go Fishing For the Fish Clip When If Goes Where Magnet Won’t Reach

I get the fish clip head around the lower master link pin and the tail pointing at the groove on the upper pin. I use one screw driver to help hold the fish clip on the backing plate and the other pressed against the head to push it up so the tail will slide in the groove of the upper pin. It takes a lot of force and some minor repositioning to get it snap into place.

Pushing Fish Clip Up With Screw Driver Blade (Bottom of Picture)

I confirm that the bronze back plate is tight on the pins, the fish clip is flat on the plate, and the tail and head are fully inserted into the grooves on the pins. I don’t want the fish clip to come loose.

Fish Clip Looks Flush With Bronze Back Plate

Confirming Fish Clip is Tight on Both Pins and Secure

The new master link is black so it is easy to find on the chain.

New Master Link Installed (Black Link)

I confirm once again that the crankshaft and camshaft timing marks are still aligned. The mark on the crankshaft nose looks a bit off in the picture, but that’s due to not being exactly in front of the engine when I took the picture. The picture underneath shows no change in the alignment marks on the two sprockets. It is hard to see the paint on the tooth of the upper crankshaft sprocket but it is visible towards the root of the tooth.

Its a good idea to oil the crankshaft sprocket and camshaft sprocket teeth with some oil after you get the new chain installed. They get lubrication when the high oil pressure relief valve above the crankshaft sprocket opens and lets oil drain over them. They may not get lubrication right away when you first start the engine.

Install Crankshaft Front Bearing Seal and Camshaft Seal

I use some steel wool to clean the inside bores of the holes for the seals. Then I use an alcohol pad to remove any dirt.

Cleaning Inside Edge of Crankshaft Seal Hole

I use a drop of engine oil on a finger and spread it on the outside of the crankshaft bearing seal.

A Drop of Oil

Light Oil on Outside of Crankshaft Seal

I can press the seal into the bore with my fingers without heating the case. I check the seal depth so it is flush with the front of the inner timing cover.

Pushing in Crankshaft Seal by Hand

Pushing in Crankshaft Seal by Hand

Checking Crankshaft Seal Is Flush With Outside of Cover

I follow the same procedure with the cam shaft seal. I check that the edge of the seal is flush with inside of the inner timing cover.

Light Oil on Outside of Camshaft Seal

New Camshaft Seal From Back of Cover

Checking Camshaft Seal Depth is Flush With Back of Cover

Install New Inner Timing Cover Gasket and Two “Donut” Gaskets

It is very important that the gasket sealing surfaces on the inner timing cover and engine block are cleaned so there is no old gasket material or debris. They and the gasket should be completely oil free. The gasket has an adhesive that makes an oil tight seal, but it won’t stick if there is oil on the mating surfaces. You do NOT use gasket sealer with the inner timing cover gasket.

I use acetone to clean the mating surfaces and then follow up with alcohol swaps until the swabs showed no discoloration. I was surprised by the amount of material the alcohol swab picked up after I had used the acetone. I use an alcohol swap to clean the bore the nose bearing race slides into on the back of the cover.

Alcohol To Clean Gasket Seam of Inner Timing Cover

Alcohol Wipe Cleaning Gasket Surface on Engine Block

Alcohol Wipe Cleaning Inside of Crankshaft Nose Bearing Bore

I put on a clean pair of rubber cloves and then I hang the gasket on the three engine studs.

Mounting Gasket with Clean Rubber Gloves

There are two “donut” gaskets that fit over the top two bolts that mount the inner timing cover on the block. They don’t seal oil but are required so the inner timing case fits squarely on the engine block. I used a little grease to hold them in place, actually some of the left over lard :-).

Gasket “Donut” on Top Mounting Holes in Engine Block

Location of (2) Gasket “Donuts” on Engine Block

I am ready to install the inner timing cover. But, one more time, I confirm that the engine is at TDC and the timing marks on the sprockets are aligned. I also remove the masking tape and rags I put into the engine openings. I check the timing chain tensioner C-clip is on its groove and the crankshaft front bearing carrier nut is at the correct torque.

Install Inner Timing Cover

The inner timing cover is heated to 250-275 F so it will slide over the outer race of the cranshaft nose bearing. I read that some people were able to slide it right on and others had problems. So I set up the Cycle Works tool to install the inner timing cover. I use the aluminum plate, the puller body and the pusher bolt with nut that threads into the crankshaft nose. I don’t need the alternator bolts to hold the aluminum plate since the pusher bolt will push the aluminum plate against the alternator boss sliding the inner timing cover on to the crankshaft nose bearing. Once again, this is the backup should the cover not slide on easily.

Orientation of Cycle Works Puller Body and Aluminum Plate

Orientation of Cycle Works Tool To Install Inner Timing Cover

I put a little lard on the outside of the crankshaft nose bearing and then put the inner timing cover in the oven and heated it to 265 F and then quickly took it into the shop and pushed it on. It slide down the crankshaft nose bearing and tight on the engine block with out difficulty. So I didn’t need to use the Cycle Works tool.

NOTE:However, it maybe a good idea to use the tool to ensure the inner timing cover is kept tight against the gasket as you run in and initially torque the Allen bolts and nuts. The inner timing cover cools while you tighten up the Allen bolts and nuts so it tightens up on the crankshaft nose bearing which could keep it from compressing the gasket completely. I don’t think that’s likely, but it would be insurance that the inner timing cover is all the way over the nose bearing and against the gasket while you torque the (9) bolts and (3) nuts.

A Little Lard on Crankshaft Nose Bearing Outer Race

Heating Inner Timing Cover in Oven

I quickly threaded the (9) Allen bolts and (3) Allen nuts finger tight and then torqued them to 70 INCH/Lbs (NOT FOOT POUNDS) in a criss-cross pattern to evenly draw the inner timing cover onto the engine block to compress the gasket evenly.

Running in Bolts on Inner Timing Cover

Torquing Bolts on Inner Timing Cover

There is enough play side-to-side play of the inner timing cover on the mounting bolts that the camshaft seal can be off center and leak oil. The advice I received was to use a caliper to measure the distance between the camshaft and the edge of the camshaft seal bore and then center the cover around the camshaft. My caliper legs aren’t long enough to reach the bottom of the camshaft seal bore and it has a sloping surface. So after I removed the camshaft seal from the inner timing cover I measured the camshaft diameter and the seal bore diameter. The camshaft is 9 mm and seal bore is 25 mm. The difference is 16 mm. One half this, or 8 mm, is the distance between the cam and the edge of the seal bore. That’s the same as the diameter of an M8 bolt (or very close). I chose one long enough so the head would clear the end of the camshaft. I place the bolt against the camshaft and slowly push it around the shaft to see how close it comes the edge of the seal bore. The M8 bolt becomes a gauge block to accurately measure the distance between the camshaft and the seal bore so I can verify it is even all the way around.

I show how I use the M8 bolt to check the inner timing cover alignment around the camshaft seal in this short video clip. It turned out my cover was centered so I didn’t have to adjust it.

Using M8 Bolt To Check That Camshaft Seal is Centered

To ensure that the cover is tight on the gasket, I heated around the crankshaft seal and then torqued the bolts to 72 INCH/Lbs (NOT FOOT POUNDS).

Heating Case Near Crankshaft Nose Bearing To Seat Inner Cover Tightly

Install Engine Electrical Components

I’m installing a new diode board, alternator rotor and replacing the three alternator phase wires, the “Y” wire that goes from the right side of the alternator to the right side of the diode board and the “red” wire that goes from the left side of the diode board to the screw terminal on the starter solenoid.

Install New Diode Board

Here is the new diode board from Euro Motoelectrics.

New Diode Board and Original Allen Bolts

Installing the diode board means putting the engine electrical harness back as well since some one of it’s connections go to the diode board. I am putting a new rubber grommet on the harness. I cut the old one off. There is no way to push the new grommet on the harness so I cut it and wrap it around the harness.

Removing Old Rubber Grommet

I install the new “red” wire on the inside left terminal spade and the black wire on the outside larger spade.

“Red” Wire (Inside) and Large Black Wire (Outside) on Right Side of Diode Board

I install the two blue wires on the one of the two spades on the back right side of the diode board. Both spades are electrically connected so you can connect to either one.

Two “Blue” Wires on Back of Diode Board

I install the three alternator phase wires (red, blue, black) on the three center terminals on the back of the diode board. The new wires are separate, not encased in a rubber terminal as done with the old wires. It does not matter what order these wires go on the spades.

3-Phase Wires Plug Into Back, Center Terminals of Diode Board-Order Does Not Matter

I put the three alternator phase wires through the center opening of the inner timing cover and back out the bottom so they route to where the alternator cover will mount near the end of the crankshaft.

Routing of Alternator 3-Phase Wires

I route the “red” wire on the left side of the diode board through the center opening of the inner timing cover toward the starter solenoid.

“Red” Diode Board Wire Routing

The red wire from the right side of the diode board and the black wire in the wiring harness go on the starter solenoid.

“Red” and Black Wires Going to Starter Solenoid

I mount the ring terminal of the red wire and the black (+) battery wire on the threaded stud of the starter solenoid. I am carefully to route them so they won’t chaff on the sharp edges of the engine and inner timing cover. Then I connect the small black wire to the spade of the starter solenoid and put some dielectric grease on the solenoid terminals to prevent corrosion.

I make sure all the wires stay inside the four studs the diode board mounts on and push the diode board backwards on the mounting studs and then secure it with the four Allen bolts. I put on the new grommet for the engine wiring harness: I will get it positioned when I install the front engine cover. I also replace the grommet on the black (+) battery wire by treading it over the ring terminal that goes on the battery post and sliding into place.

Orientation of Diode Board Wires Between Four Mounting Studs

Install Condenser and Points

The Dyan III electronic ignition does not use the condenser, but I install it so I can quickly install the original mechanical points should the Dyna III fail. The black wire going to the coils goes on one condenser terminal. If I have to install the mechanical points, the points wire will go the other terminal.

Condenser Mounting in Strap

Rubber Points Wire Cover Installed

Condenser and Coil Wire Installed

Then I install the Dyan III points plate aligning it with the index mark I scribed and then the timing advance cam so the flat aligns with the flat on the cam shaft.

I replace the old rubber gasket in the groove of the raised housing around the points. I use silicone seal to hold it in place and after it dries, I trim off the extra gasket with diagonal pliers.

Dyna III Points Plate Installed

Points Advance Unit With Locating Flat

New Rubber Gasket for Points Housing

New Points Housing Seal Will Get Trimmed

Install New Alternator Brushes

The terminals on the alternator cover are grungy and corroded so I clean them up with some 600 grit sand paper and spray them with contact cleaner.

Dirty Alternator 3-Phase Terminals

Cleaning Underside of Alternator 3-Phase Terminals

I replace the black “Y” wire with the new one and clean the terminal spade.

New Alternator “Y” Wire Goes On Left Side of Diode Board

I remove the springs holding the brushes in the white plastic holders and unscrew the brush terminals, remove them and clean them.

I use a 260 watt soldering iron to remove the brush pigtails from the terminals. I use a small drill bit to clean out any solder inside the terminal hole so the new brush pigtail will easily fit.

260 Watt Soldering Gun

Unsoldering Old Brush From Terminal

I tin the new brush pig tail with solder, insert the old insulator on the lead and then solder the lead to the alternator cover terminal.

Tinning New Brush Pigtail

Old Insulator and New Brush

Old Insulator on New Brush Pigtail

Soldering Brush Pigtail in Terminal Hole

Note that the brush pigtail should be oriented to the side, as shown, so there is enough play in the pigtail to let the brush go to the bottom of the holder.

Proper Orientation of Soldered Brush Pigtail to the Side

I slide the new brushes into the white plastic holder so the pigtail is on the inside of the brush in the groove of the holder. I wind up each coil spring one turn and place the end on top of each brush.

Orientation of Brush Pigtails To Inside of Holder

Install New Alternator Rotor

Here is the new rotor with the protective black plastic cap on the copper slip rings. This size rotor fits the /6 series alternator. BMW changed the output of the alternator across the airhead models so be sure you get the correct size alternator for your model.

New Enduralast Rotor

New Enduralast Rotor with Sip Rings Protective Cover Removed

The old alternator with 40 years and 105,000 miles on it (left) and the new Euro Motoelectrics alternator (right). I use metal cleaner to clean the copper slip rings before installing it.

Original BMW (Left) and New Enduralast Alternator Rotor (Right)

I learned that the screw threads in the Euro Motoelectrics rotor are different from the stock BMW alternator rotor. So, the stock hardened rotor removal bolt will not work. Euro Motoelectrics provides a suitable hardened bolt and extension piece with the rotor. DO NOT LOOSE IT. I put mine in a small plastic bag and marked it and put it with the one I use for the stock BMW rotor.

EnduraLast Rotor Removal Tool-Different Thread From Stock BMW Tool

The taper on the nose of the crankshaft has to be completely clean with no oil or finger prints on it. I clean mine with metal polish to remove the discoloration and then wipe it down with alcohol swabs until they show no discoloration. I also wipe the inside of the tapered bore in the new alternator rotor to be sure it is clean and oil free.

Dirty Crankshaft Nose

Cleaned Crankshaft Nose With Metal Polish

Alcohol Wipes Remove Any Traces of Oil From Crankshaft Nose

I put the rotor on the crankshaft nose and thread the rotor bolt in. I use the oil filter wrench to prevent the crankshaft from turning and torque the bolt to 12-14 Ft/Lbs.

Tightening Alternator Rotor Bolt While Holding with Oil Filter Wrench

New Alternator Rotor Installed

Install Alternator Cover and Wiring

It is a good idea to clean the outside metal lip of the stator housing and the inside of the three raised ribs, or bosses, it slides into before installing the cover. I slide the alternator cover and stator wiring as a unit over the rotor being careful that the stator wires don’t snag on the edge of the rotor and I don’t stretch the wires going from the stator to the alternator cover. I push up on the brushes so they will clear the slip rings as I slide the alternator housing over the rotor.

Lifting Brushes Up On to the Slip Rings

I align the alternator housing with the three bolt holes in the inner timing cover and position the edge inside the three raised bosses.

Alternator Cover Started in Bushing

It is a good idea to put a dab of anti-seize on the three Allen bolts that secure the alternator cover. I insert all three and finger tighten them. Then I use my socket wrench to tighten each a 1/4 turn so the alternator housing goes on square with the bosses. When it is all the way in, I snug the the bolts tight, but not overly tight so I don’t strip the threads in the aluminum inner timing cover. There is no torque setting for these bolts.

Alternator Cover Installed

I attach the two wires, the black one and the blue/black strip one, to the top brush spades, the three 3-phase wires to the three spades at 5:00 (they can go in any order). I put the other end of the black “Y” wire on the left side of the alternator on the left side of the of the diode board.

Alternator and Wiring Installed

Black “Y” Wire (Yellow Insulator) Attached to Left Side of Diode Board

Here is the finished product after the engine electrics are installed.

Engine Electrics Installed Ready for Front Cover

So, the beer lamp is lit. Qwaff one if you have ’em :-).

All Done – Time to Relax

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Wow. This looks like a very complicated repair. I don’t know if I would want to do this myself. That being said, I did my rear engine seal because of visible oil leaking from the rear transmission shelf and with all the proper tooling it worked out ok. No visible oil now. My 1976 R75/6 has 116000 miles on it. I’m wondering what condition would precipitate a timing chain replacement? The bike runs pretty good for 40 years old. Sometimes it has a tendency to stall when I come to a stop but I believe this is just a carb issue(idle low). I believe I would do a valve job first and am planning that in the coming weeks. With our low Canadian dollar, parts sourced from USA will be expensive but hey, look at the money I’ll save in labour and the satisfaction of doing it yourself. this was a great how to. Thanks.

Yes, there is a bit of detail in the procedure, but with the right tools, and doing one thing at a time, it’s not difficult. Or, said differently, two old sayings come to mind:

– You can fix just about anything if you have the right tool
– It’s easy when you know how

I hope this procedure helps with both of these :-). That said, I wanted to be detailed so anyone can make an informed decision if this seems like work they could tackle on their own, or not.

The timing chain wear is typically in the teeth of the crankshaft sprocket more than stretching of the chain or wear of the camshaft sprocket. Also, the chain tensioner plastic wears through eventually. The result of the sprocket wear is valve timing changes and possible chain noise coming from the timing cover if the tensioner becomes weak.

By cutting that timing chain as you did, you irretrievably contaminated the bearing AND the seals. I understand you intended to replace these items with new, but another owner might have hoped to re-use these parts, especially the bearing. But be aware that no amount of cleaning/flushing would be adequate to decontaminate those items after the Dremel cutting.

Also, striking or pressing on an unsupported ball-bearing race will not damage the bearing cage. It will irreparably damage the actual ball races through a process called “ball-denting”. Ball bearings actually are (almost) point to point contact internally. So any impact force on the unsupported race is transmitted through the race to the ball point and back to the other race which created and actual dent in one or both of the races.

If the chain must be cut with abrasive wheels a method must be found to very thoroughly protect seals and bearing from any possible contamination by abrasives. Perhaps cutting at the very lowest point on the chain would help.

Thanks for reading over this write-up and providing the detailed commentary (both of them) about bearings. I would rent some large bolt cutters at my local tool rental dealer for cutting the chain on the next project. There is a lot of shrapnel with the Dremel cutoff wheel and that’s always troubling. Since I am also replacing the oil pan gasket I will be able to ensure nothing managed to get past the covered openings. And as I noted in the writeup, this job SHOULD include replacing all seals and the nose bearing anyway, so there should be no issue with debris in the bearings or seals.

Another bearing minutia concern that might be interesting. When assembling the inner cam-chain case over the bearing… You did it right because the heated cover slipped completely home over the bearing. But in a case where the owner didn’t quite get it all the way on, it would be normal to use the case bolts and nuts to pull the cover home, snugging the case up those last few 1/16ths to a nice tight fit.

The problem with that is that the bearing is now axially pre-loaded. It’s clamped axially between the inner and outer race by the friction between the case bore and camshaft bore. That bearing is a C3 internal clearance (looser than normal) to compensate for the normal high temperature operational environment. But unless the bearing is able to shift axially into a normal radial concentricity, it will fail prematurely.
So as you stated, be sure that the bearing and sprocket are fully seated on the shaft AND the cover is pushed fully home before it cools and tightens up on the outer race of the bearing.

Thanks for taking the time to document this project so exhaustively; it makes a great companion to Snowbum’s information on the same job, and I am studying both as I prepare to pull the block out of my 1976 R60/6 for a timing chain while the frame is at the powdercoater.

One question – why did you choose lard as a lubricant for fitting the new sprocket? I have never heard of it used in this application before and was curios as to the advantage.

It has useful properties compared to engine oil when assembling steel parts. It sticks well and stays put and also tends to be sticky so parts stay where you align them before pressing them on. And, it’s a by-product from cooking bacon, so it’s got that going for it as well. 🙂

One more question – what led you to determine that the bronze plate on the new master link was the back plate rather than the center plate? I was operating on the assumption that the black one would be the back plate so that both sides of the master link would be black…

Brook, thank you this fantastic article. My friend and I are in the process of rebuilding a 1976 R90S and have completely pulled it apart. I intend to print your entire article, put each page is a protective plastic sheet and the collection in a binder as our “bible” for this portion of the work. It really fills in the numerous gaps in the Clymer manual and will surely help us avoid the many “traps” waiting for less experienced engine builders such as ourselves.
Many thanks!
Frank

I have all the parts needed to replace the front timing chain on my wonderful ole 1973 R75/5 with ” very very high mileage ” !….and this step by step help sure will be their on my lap top as i perform the job theirs a few things i fear about the whole job and i want to do this job right………Thanks so much